This invention relates to sizings for glass fibers and particularly to the sized glass fibers which are combined with aqueous media, such as cementitious products, including sodium silicate, calcium silicate, cement, concrete and gypsum to form reinforced inorganic matrices and to form paper products, such as sheet material.
The prior art has employed glass fibers at low concentrations to reinforce inorganic media but these glass fibers were generally sized with starch-containing materials. These sized glass fibers however, were not without their problems, such as lack of filamentization of the glass fibers from their bundles, whereby the potential of the available surface area of the glass fibers to serve as a reinforcement could not be attained. Furthermore, attempts to use glass fibers as a reinforcement in aqueous media in the form of textured yarn, which did not filamentize but which had greater surface area per unit length exposed to the media than untextured yarn in order to overcome the above problems, were expensive. However, these textured yarns, although providing loops and voids for mechanical locking of the glass fibers into the matrix, were not realizing their effective potential surface area, because of lack of filamentization of the textured yarns.
The above problems are overcome by the concepts of this invention, wherein the sized glass fibers remain integral during processing operations, such as drying, chopping, packaging and shipping. Further processing steps which the sized glass fibers may be exposed to include the steps of running a strand from a package and combining the same with a multiplicity of other strands from other packages and forming a roving, followed by a subsequent collection of the roving on a package and/or chopping the roving to length. The roving, even though it comprises a multiplicity of bundles of glass fibers, has the capability of complete filamentization during blending and mixing with the aqueous inorganic medium to maximize its reinforcement potential. The sized glass fibers of this invention are used at relatively high concentrations of from about 1 percent to about 99 percent by weight as compared to the prior art, without clumping of the glass fibers occurring upon mixing the glass fibers into the media.
U.S. Pat. No. 3,716,386, issued on Feb. 13, 1973, discloses a process for preparing a fibrous cementitious mix, wherein fibers (glass) of the mix are immersed in a solution of polyethylene oxide or methyl cellulose prior to incorporation of the glass fibers into the mix. In this teaching, however, the fiber treatment is not a sizing applied at the time of forming the glass fibers, but rather is a post-treatment or secondary treatment, thereby indicating that the glass fibers have a sizing thereon in addition to the post-treatment. It is not known whether that sizing is water soluble, although the post-treatment is water soluble.
The concepts of the present invention, however, require that the sizings comprise a water soluble polymer, and that the glass fibers be preferably dried prior to use. Upon incorporation of the sized glass fibers of this invention into an aqueous media, time is required for the polymer to absorb sufficient water to cause solvation, which thereby induces filamentization of the glass fibers from the strands.
The sizings of this invention provide processing and end-product properties to the sized glass fibers so that the glass fibers may be collected on a package, dried, chopped, or be combined with other strands to form a roving. Additionally, upon incorporation into an aqueous media, the sized glass fibers in the form of strands, bundles, and rovings, undergo instantaneous or delayed filamentization, whichever is desired for a particular process. In either situation, filamentization of the sized glass fibers is achieved without clumping.